It has recently been shown that a mouse line that expresses Cre under control of the promoter for the transcription factor Phox2a can be used to reveal some of the ALS neurons belonging to each of the populations described above.5,25 Crossing this Phox2a::Cre line with appropriate reporter lines, results in permanent expression of fluorescent proteins in these cells, thus allowing them to be identified and labelled, without the need for retrograde tracing. This evidence concerns the gene PHOX2A and amyotrophic lateral sclerosis.